Auxiliary contact structure with arc suppressing means



April 16, 1968 J. M. RAMRATH AUXILIARY CONTACT STRUCTURE WITH ARCSUPPRESSING MEANS 3 Sheets-Sheet 1 Filed Oct. 20, 1965 5214034115 11 Jpn45a 29 7 @XXpB April 16, 1968 J. M. RAMRATH 3,378,661

AUXILIARY CONTACT-STRUCTURE WITH ARC SUPPRESSING MEANS Filed Oct. 20,1965 3 sheetssheet F:

g zmz/zg April 16, 1968 J. M. RAMRATH 3,378,661

AUXILIARY CONTACT STRUCTURE WITH ARC SUPPRESSING MEANS Filed Oct. 20.1965 3 Sheets-Sheet 5 g 3 I 30/ 2 32 W. 6152mm}? JQMOM United StatesPatent 3,378,661 AUXILIARY CONTACT STRUCTURE WITH ARC SUPPRESSING MEANSJoseph Maria Ramrath, Mattapan, Mass., assignor to Allis-ChalmersManufacturing Company, Milwaukee, Wis.

Filed Oct. 20, 1965, Ser. No. 498,209 4 Claims. (Cl. 200-150) Thisinvention relates generally to electric circuit breakers andparticularly to oil circuit breakers of the fluid blast type, althoughnot necessarily limited thereto.

Some oil circuit breakers comprise one pair or a plurality of seriesconnected pairs of separable contacts for each phase or line of acircuit being protected. In practice each pair of contacts is adapted tooperate inside the housing of an arc interrupting device which confinesthe are formed between the contacts. Usually, fluid blast means areprovided in the housing to aid in extinguishing the arc.

In one well known type of oil circuit breaker a pair of spaced apartline terminals extend into the top of a tank containing a body of fluidsuch as oil and a pair of main arc extinguishing devices are submergedin the fluid. Each main arc extinguishing device comprises an arcconfining housing in which a stationary contact is mounted and thelatter is connected to one of the line terminals. A reciprocably movableelectrically conductive cross arm is located inside the tank and isprovided with a pair of spaced apart bayonet type movable main contacts.Each movable contact is adapted to cooperate with the stationary contactwithin the housing of one of the main arc extinguishing devices. Thus,when the circuit breaker is closed a U-shaped current path or circuit isestablished between the line terminals.

In some circuit breakers of this type, four or more main arcextinguishing devices are used instead of the two described but theU-shaped current path retains its identity.

It is an object of the present invention to increase the continuousandshort circuit current carrying capacity of such circuit breakers bymeans which economically exploit the design and inherent operatingcharacteristics thereof.

Another object is to increase both the normal and short circuit carryingcapacity of such circuit breakers by providing an additional or secondcurrent carrying circuit in parallel with the aforementioned or firstU-shaped circuit.

Another object is to locate the second circuit with respect to the firstcircuit so that electromagnetic forces interacting between the twocircuits cause a large proportion of continuous current to flow throughthe second circuit.

Another object is to provide a second circuit which comprises one ormore pairs of auxiliary contacts connected in shunt with the maincontacts in the main are interrupters and located generally on theinside of the first U- shaped circuit.

Another object is to have the auxiliary contacts open before and closeafter the main contacts so that the main burden of arc interruption ishandled by the main contacts.

Other objects and advantages of the invention will here inafter appear.

The accompanying drawings illustrate several preferred embodiments ofthe invention but it is to be understood that the embodimentsillustrated are susceptible of modifications with respect to detailsthereof without departing from the scope of the appended claims.

In the drawings:

FIG. 1 is an elevational view, partly in section, of one embodiment ofan oil circuit breaker employing the present invention;

3,378,661 Patented Apr. 16, 1968 ice FIG. 2 is a top plan view of aportion of the circuit breaker taken along line II-II of FIG. 1;

FIG. 3 is a cross-sectional view of an auxiliary contact structure orare extinguishing device shown in FIG. 1, showing it in open position;

FIG. 4 is a view similar to FIG. 3 but shows the auxiliary contactstructure in closed position;

F168. 5, 6 and 7 are diagrammatic showings of a portion of the electriccircuitry of the circuit breaker shown in FIGS. 1 and 2, and show it inclosed, partially open, and fully open positions, respectively; and

FIG. 8 is a diagrammatic showing of another embodiment of an oil circuitbreaker employing the present invention.

Referring to FIG. 1, there is shown an oil circuit breaker incorporatingthe present invention and having a tank 10 which is filled to a level 12with an arc extinguishing fluid such as oil. A pair of line terminalbushings 14 and 16 comprising electrical conductors 18 land 20,respectively, for connection to a power line being protected extend intotank 10. Arc extinguishing assemblies 22 and 24 are suspended from theinner ends of the terminal bushings 14 and 1-6, respectively. Theassemblies 22 and 24 are understood to be similar to each other,therefore, only the former will be described in detail.

Referring to FIGS. 1 and 2, assembly 22 comprises upper, intermediateand lower electrically conductive platform castings 26, 28 and 30,respectively. Upper casting 26 is electrically and mechanicallyconnected to conductor 18 of terminal bushing 14. Intermediate casting28 is spaced from and mechanically supported on upper casting 26 bymeans of insulating supports such as support 32. Lower casting 30 isspaced from and mechanically supported on intermediate casting 28 bymeans of insulating supports which are understood to be similar tosupport 32.

Upper and lower main arc interrupters 36 and 38 depend from the upperand intermediate castings 26 and 28, respectively, and, as FIGS. 5, 6and 7 show, comprise stationary contacts 40 and 42, respectively, whichare electrically connected to the upper and intermediate castings,respectively. Reference may be had to Patent Number 3,067,307 for FluidBlast Interrupting Device for Oil Circuit Breakers issued December 4,1962, to I. M. Ramrath and asigned to the same assignee as the presentapplication for a detailed description of an interrupter of a typesuitable for application as the main arc interrupters herein referredto.

Upper and lower auxiliary contact structures 44 and 46 are mountedadjacent the main interrupters 36 and 38, respectively, and, as FIGS. 5,6 and 7 show, comprise stationary contacts 48 and 50, respectively,which are electrically connected to the upper and intermediate castings26 and 28, respectively.

Upper auxiliary contact structure 44 is similar to lower auxiliarycontact structure 46, therefore, only the former will be described indetail. As FIG. 3 shows, contact structure 44 comprises a metallic topsection adapted for electrical and mechanical connection to upperplatform casting 26. Top section 100 is provided with oil refill ports102 in the side walls thereof. A dome shaped piston 104 is locatedwithin top section 100 and is provided with openings 106 for equalizingoil pressure on each side thereof and with a vent 108 through the topthereof. Piston 104 is provided with a piston ring 105. A nonmetallicpiston push rod 110 has one end bearing against piston 104 and its otherend abutting against a movable auxiliary contact 78, hereinafterdescribed. Push rod 110 is adapted to maintain vent 108 closed when itbears against piston 104. A push rod driving spring 112 is disposedbetween a portion of top section 100 and push rod 110. A piston drivingspring 114 is disposed between a portion of top section 100 and piston104. Stationary contact 48 which is located in contact structure 44comprises a contact housing 116 in which a cluster of spring biasedcontact fingers 118 are located. Contact housing 116 comprises a spidersection 120 which adapts it for electrical and mechanical connection totop section 100.-The lower end of top section 100 is closed by aninsulating bafiie plate 122 having a hole 124 for accommodating movableauxiliary contact 78.

High ohmic value resistors 52 and 54 are electrically connected,respectively, between the upper and intermediate castings 26 and 28 andbetween the intermediate and lower castings 28 and 30.

An electrically conductive cross bar 56 which is re ciprocably movablevertically (with respect to FIG. 1) by an insulating rod 57 is providedat its extreme ends with upwardly projecting or bayonet typeelectrically conductive movable contacts and movable contact operators,hereinafter described. Preferably, cross bar 56 comprises two separatemembers 56a and 56b to enhance thermal conductivity therefrom. The endof cross bar 56 which is associated with are extinguishing assembly 22comprises a movable lower main contact 58 and a movable lower auxiliarycontact 60 and a pair of contact operators 62 and 64.

Lower casting 30 of assembly 22 is provided with a pair of slidingcontacts 66 for accommodating the movable contacts 58 and 60. Lowercasting 30 is also provided with a pair of openings 68 in alignment withthe contact opera:

tors 62 and 64. The contact operators 62 and 64 cooperate withelectrically nonconductive contact push rods 72 and 74, respectively.The push rods 72 and 74 are connected to and operate a reciprocablymovable upper main contact 76 and a reciprocably movable auxiliary upperauxiliary contact 78, respectively, which extend through a pair ofsliding contacts 80 and 81, respectively, mounted on intermediatecasting 28. Contacts 76 and 78 extend into main arc interrupter 36 andauxiliary contact structure 44, respectively, when the circuit breakeris closed.

Push rod 72 and its attached movable upper main contact 76 are enclosedin an insulated housing 79 shown in FIG. 1 and suitable biasing means,such as a spring 83, in housing 79 tend to bias the push rod and uppermain contact downwardly with respect to FIG. 1. It is to be understoodthat similar provisions are made for housing and biasing the other pushrods and their attached movable upper contacts.

When the circuit breaker is fully closed, as shown in FIGS. 1 and 5,there are two parallel U-shaped current parts between the conductors 18and 20 of the terminal bushings 14 and 16, respectively, with one pathbeing located substantially within the other.

The outer and longer path extends from conductor 18, through uppercasting 26, stationary contact 40 of upper main interrupter 36, movablecontact 76, intermediate casting 28, stationary contact 42 of lower maininterrupter 38, movable contact 58, cross arm 56, movable contact 58a,stationary contact 42a of lower main interrupter 38a, intermediatecasting 28a, movable contact 76a, stationary contact 40a of upper maininterrupter 36a, upper casting 26a, to conductor 20.

The inner and shorter path extends from conductor 18, through uppercasting 26, stationary contact 48 of upper auxiliary contact structure44, movable contact 78, intermediate casting 28, stationary contact 50of lower auxiliary contact structure 46, movable contact 60, cross arm56, movable contact 60a, stationary contact 50a of lower auxiliarycontact structure 46a, intermediate casting 28a, movable contact 78a,stationary contact 48a of upper auxiliary contact structure 44a, uppercasting 26a, to conductor 20.

No substantial current flows through the impedances 52, 54, 52a or 54awhen the circuit breaker is closed.

Current flow through both paths is accompanied by generation of amagnetic field around each path and these magnetic fields interact tocause a large portion of the current flow through the circuit breaker totravel through the inner path hereinbefore described. More specifically,the outer path is longer than the inner path and therefore has greaterinductance and the larger portion of current will flow through theshorter inner path. Since the inner path includes the auxiliary contactstructures which are adapted to be more readily cooled by the oil in thecircuit breaker than the main interrupters, larger currents can becarried by the inner path than would otherwise be the case if the samecurrent were channeled through the outer path. 8

FIG. 8 shows another embodiment of the invention wherein only one pairof main arc interrupters 36b and 36c and one pair of auxiliary contactstructures 44b and 440 are employed in a circuit breaker. The maininterrupter and auxiliary contact structures shown in FIG. 8 areunderstood to be similar to the corresponding structures hereinbeforedescribed in connection with FIGS. 1-7. Main arc interrupters 36b and360 comprise stationary main contacts 40b and 400, respectively, and theauxiliary contact structures 44b and 440 comprise stationary auxiliarycontacts 48b and 480, respectively. A reciprocably movable bridge 56a isprovided having movable main contacts 76b and 76c and having movableauxiliary contacts 781) and 780. Two platform castings 26b and 260 areprovided from which the main and auxiliary interrupters depend.

When the circuit breaker is in the closed position shown in FIG. 8, anoutermost and longer first U-shaped circuit is established from platformcasting 26b, through contacts 40b and 76b, through bridge 56a, andthrough contacts 76c and 40c, to platform casting 26c.

Furthermore, an innermost and shorter second U-shaped circuit isestablished from platform casting 2612, through contacts 481) and 78b,through bridge 56a, and through contacts 78c and 480, to platformcasting 26c.

It is to be understood that the auxiliary contacts in the auxiliarycontact structures 78b and 780 are adapted to open before and closeafter the main contacts in the main arc interrupters 36b and 36c.

. If preferred, suitable shunt resistors could be employed with theembodiment disclosed in FIG. 8.

Assuming that the circuit breaker is closed as shown in FIGS. 1 and 5and that a fault occurs which causes it to open, the following sequenceof operations occurs. Rod 57 moves cross bar 56 downwardly therebycausing all the movable contacts and contact operators on the cross barto start their withdrawal. As FIG. 6 shows, the contacts in the innerpath, i.e., those contacts in the auxiliary contact structures 44, 46,44a and 46a, open shortly before the contacts in the main interrupters36, 38, 36a and 38a. All current flow is now carried by the outer path.As cross bar 56 continues to move downwardly, the contacts in the maininterrupters 36, 38, 36a and 38a open simultaneously and the impedances52, 54, 52a and 54a, respectively, are then connected in parallel withthe arcs produced in the main interrupters to equalize circuit recoveryvoltage across the main interrupters upon opening. By the time cross bar56 moves to the fully open position shown in FIG. 7, the arcs areextinguished and the current flow through the impedances ceases sincethe movable contacts 58 and 60 are disengaged from the sliding contactsin the lower castings 30 and 30a.

More specifically, as regards operation of auxiliary interrupter 44,during the initial portion of the opening stroke of auxiliary bayonetcontact 78 is also accelerated by the forces exerted downward againstthe tip thereof by both piston push rod spring 112 and the piston spring114. However, after a fraction of an inch of piston stroke, the loweredge of piston ring 105 seals off the bottom of the refill ports 102.After this occurs, any further downward motion of piston 104 and pistonring 105 can be accomplished only by displacement of the oil in topsection of structure 44. At this point, the velocity of the piston isvery greatly reduced since the limited area of orifice 124 betweenbafiie plate 122 and moving auxiliary bayonet contact 78 allows verylittle oil to flow out of structure 44 as long as auxiliary bayonetcontact 78 penetrates the baflie plate.

However, during the opening stroke the travel of piston push rod 110 isnot hindered by the travel of piston 104 nor is the spring force actingon the piston push rod in any way reduced by piston travel as is thecase in US. Patent No. 3,076,080 to I. M. Ramrath, Fluid BlastInterrupting Device for Oil Circuit Breakers Employing AuxiliaryContact. Thus, when the velocity of piston 104 is reduced by theimpedance of the oil beneath it, piston push rod 1110 continues to bedriven downward by piston push rod spring 112. Piston push rod 1110continues to accelerate auxiliary bayonet contact 78 even after theelectrical separation of the auxiliary contacts. This follow throughaction terminates only when the flange at the upper end of piston pushrod 110 comes into contact with the top of the stationary contacthousing 116 to prevent any further push rod travel. At this point, thelower end of piston push rod 110 approaches the upper surface of baflleplate 122, forming a relatively small annular orifice between the bottomend of the piston push rod and the upper surface of the baffle platethrough which oil from auxiliary interrupter 44 may flow, and throughwhich any are between the stationary auxiliary contacts and the movingauxiliary contact must pass. The piston push rod stroke is terminatedonly after the auxiliary contacts have developed an appreciableseparation, approximately A" in an actual embodiment. In this mannerauxiliary bayonet contact 78 receives an accelerating force from pistonpush rod spring 112, sufficient to assure that the velocity of auxiliarybayonet contact 78 does not fall below that of bayonet 76 in interrupter36. It also assures electrical separation of the auxiliary contacts 48and 7 8 at a precisely controlled period of time before the associatedmain contacts 40 and 76 of main interrupter 36. This assures that thegap between the auxiliary contacts will at all times be greater than thecorresponding gap between the main contacts which are electrically inparallel. As the piston continues to be driven downward by the forcegenerated by the piston spring, it pressurizes the oil beneath it. Theoil pressure drives the oil inward toward the lower tips of thestationary contact fingers 118 and thence through annular orifice 124and out into the tank. As the oil is forced through orifice 124, itimpinges on any are which may tend to persist between the auxiliarycontacts 118 and 78 after their separation. This action subjects the arcto an oil blast which causes a turbulent mixture of the arc plasma withthe cold oil driven in from the cylinder. The resulting deionization ofthe are products causes a rapid extinction of the arc. After the arc isextinguished, the continuation of a flow of fresh oil through orifice124 flushes any gas from the gap between the auxiliary contacts 48 and78 assuring the maintenance of a high dielectric strength of the gap.

On reclosing of the circuit breaker under load from the position shownin FIG. 7, the contacts in the auxiliary contact structures 44, 46, 44aand 46a must close within one quarter of a cycle of the contacts in themain interrupters 36, 38, 36a and 38a in order to distribute the loadand to prevent high magnetic blowofi of the main contacts as the maincontacts continue to close. The main contacts continue to move to finalclosed position after the auxiliary contacts are closed.

As auxiliary bayonet contact 78 penetrates hole 124 in baflle plate 122,it is guided into axial alignment with the cluster of stationarycontacts to minimize bouncing of the fingers when contact is made. Theupper tip of auxiliary bayonet contact 78 comes into physical contactwith the lower end of piston push rod 116. As it continues its upwardmovement, it drives piston push rod 110 upward thereby compressingpiston push rod spring 112. Piston push rod 110 also bears againstpiston 104 forcing it and piston ring 105 upward, compressing pistonspring 114. Immediately before electrical contact is established betweenthe auxiliary contacts 78 and 48, the parallel contacts 76 and 40 ininterrupter 36 are closed to establish the outer circuit thus minimizingarcing between the auxiliary contacts. Further protection againstauxiliary contact deterioration can be provided by the application of asilver-tungsten alloy on the tips of the contact fingers 118. At the endof the closing stroke, piston 104 is driven upward beyond the refillports 102 in the side of top section 100. This allows any gas fromprevious interruptions to escape and also allows the oil to establishconvection currents for effective cooling of the auxiliary contactstructure while carrying heavy continuous currents.

It is to be understood that the embodiment of the invention shown inFIG. 8 operates in substantially the same manner as that described inconnection with FIGS. 1-7, except that only one pair of maininterrupters and one pair of auxiliary contact structures are involved.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A circuit interrupter comprising a pressure confining structure foraccommodating an arc extinguishing fluid,

said structure having an end wall with an opening therethrough,

stationary contact means mounted in said structure and spaced from butadjacent to said opening,

movable contact means movable through said opening for cooperation withsaid stationary contact means,

means for closing and for separating said stationary and movable contactmeans to draw an arc to be extinguished by fluid blast action,

a spring biased piston arranged within said structure and axiallyaligned with said stationary and movable contact means,

said piston having a fluid passage therethrough,

and a spring biased piston rod movable independently of said pistonduring movement in contact opening direction,

said piston rod mounted to abut said piston and to block said fluidpassage therethrough,

said piston rod and said movable contact means being adapted to abuteach other in contact closed position,

said movable contact means being operative during circuit closingmovement to move through said opening in said end wall to abut saidpiston rod and drive said piston rod and said piston to their biasedpositions so that during a circuit opening operation said piston movesin contact opening direction for blasting fluid transversely through thespace between said stationary contact means and said opening and axiallythrough said opening,

said piston rod being independently movable during a circuit openingoperation to accelerate said movable contact means.

2. A circuit interrupter comprising a pressure confining structure foraccommodating an arc extinguishing fluid,

said structure having an end wall with an opening therethrough,

stationary contact means mounted in said structure and spaced from butadjacent to said opening,

said stationary contact means comprising a contact housing and a clusterof inwardly biased fingers in said contact housing,

movable contact means comprising a bayonet contact movable through saidopening for cooperation with said stationary contact means by engagingsaid cluster of fingers,

means for closing and for separating said stationary and movable contactmeans to draw an arc to be extinguished by fluid blast action,

a spring biased piston arranged within said structure and axiallyaligned with said stationary and movable contact means,

said piston having an opening therethrough to equalize fluid pressure onopposite sides thereof during part of its stroke,

said piston also having a fluid passage therethrough,

and a spring biased piston rod movable independently of said pistonduring movement in contact opening direction,

said piston rod mounted to abut said piston and to block said fluidpassage therethrough,

said piston rod and said movable contact means being adapted to abuteach other in contact closed position,

said movable contact means being operative during circuit closingmovement to move through said opening in said end wall to abut saidpiston rod and drive said piston rod and said piston to their biasedpositions so that during a circuit opening operation said piston movesin contact opening direction for blasting fluid transversely through thespace between said stationary contact means and said opening and axiallythrough said opening,

. said piston rod being independently movable during a circuit openingoperation to accelerate said movable contact means.

3. A circuit interrupter comprising a pressure confining structure foraccommodating an arc extinguishing fluid,

said structure having an end wall with an opening therethrough,

stationary contact means mounted in said structure and spaced from butadjacent to said opening,

said stationary contact means comprising a contact housing and a clusterof inwardly biased fingers in said contact housing,

movable contact means comprising a bayonet contact movable through saidopening for cooperation with said stationary contact means by engagingsaid cluster of fingers,

means for closing and for separating said stationary and movable contactmeans to draw an arc to be extinguished by fluid blast action,

a spring biased piston arranged within said structure and axiallyaligned with said stationary and movable contact means,

said piston having an opening therethrough to equalize fluid pressure onopposite sides thereof during part of its stroke,

said piston also having a fluid passage therethrough,

a piston rod movable independently of said piston during movement incontact opening direction,

said piston rod mounted to abut said piston and to block said fluidpassage therethrough,

said piston rod and said movable contact means being adapted to abuteach other in contact closed position,

and a biasing spring for said piston rod extending through said fluidpassage in said piston,

said movable contact means being operative during circuit closingmovement to move through said opening in said end Wall to abut saidpiston rod and drive said piston rod and said piston to their biasedpositions so that during a circuit opening operation said piston movesin contact opening direction for blasting fluid transversely through thespace between Cit said stationary contact means and said opening andaxially through said opening,

said piston rod being independently movable during a circuit openingoperation to accelerate said movable contact means.

4. A circuit interrupter comprising a pressure confining structure foraccommodating an arc extinguishing fluid,

said structure having an end wall with an opening therethrough andhaving an oil refill port in a side thereof,

stationary contact means mounted in said structure and spaced from butadjacent to said opening,

said stationary contact means comprising a contact housing and a clusterof inwardly biased fingers in said contact housing, 1

movable contact means comprising a bayonet contact movable through saidopening for cooperation with said stationary contact means by engagingsaid cluster of fingers,

means for closing and for separating said stationary and movable contactmeans to draw an arc to be extinguished by fluid blast action,

a spring biased piston arranged within said structure and axiallyaligned with said stationary and movable contact means,

said piston having an opening therethrough to equalize fluid pressure onopposite sides thereof during part of its stroke,

said piston also having a fluid passage therethrough,

a piston rod movable independently of said piston during movement incontact opening direction,

said piston rod mounted to abut said piston and to block said fluidpassage therethrough,

said piston rod and said movable contact means being adapted to abuteach other in contact closed position,

and a biasing spring for said piston rod extending through said fluidpassage in said piston,

said movable contact means being operative during circuit closingmovement to move through said opening in said end Wall to abut saidpiston rod and drive said piston rod and said piston to their biasedpositions so that during a circuit opening operation said piston movesin contact opening direction for blasting fluid transversely through thespace between said stationary contact means and said opening and axiallythrough said opening,

said piston rod being independently movable during a circuit openingoperation when said piston cooperates with said contact housing to closesaid opening in said piston and thereby slows down to accelerate saidmovable contact means.

References Cited UNITED STATES PATENTS 2,020,475 11/1935 Ronnberg200-150 2,666,118 1/1954 Ludwig et al 200150 3,205,331 9/1965 Thommen etal. 200-450 FOREIGN PATENTS 180,979 2/ 1955 Austria. 796,191 1/1936France. 1,268,547 6/1961 France.

ROBERT S. MACON, Primary Examiner.

1. A CIRCUIT INTERRUPTER COMPRISING A PRESSURE CONFINING STRUCTURE FORACCOMMODATING AN ARC EXTINGUISHING FLUID, SAID STRUCTURE HAVING AN ENDWALL WITH AN OPENING THERETHROUGH, STATIONARY CONTACT MEANS MOUNTED INSAID STRUCTURE AND SPACED FROM BUT ADJACENT TO SAID OPENING, MOVABLECONTACT MEANS MOVABLE THROUGH SAID OPENING FOR COOPERATION WITH SAIDSTATIONARY CONTACT MEANS, MEANS FOR CLOSING AND FOR SEPARATING SAIDSTATIONARY AND MOVABLE CONTACT MEANS TO DRAW AN ARC TO BE EXTINGUISHEDBY FLUID BLAST ACTION, A SPRING BIASED PISTON ARRANGED WITHIN SAIDSTRUCTURE AND AXIALLY ALIGNED WITH SAID STATIONARY AND MOVABLE CONTACTMEANS, SAID PISTON HAVING A FLUID PASSAGE THERETHROUGH, AND A SPRINGBIASED PISTON ROD MOVABLE INDEPENDENTLY OF SAID PISTON DURING MOVEMENTIN CONTACT OPENING DIRECTION, SAID PISTON ROD MOUNTED TO ABUT SAIDPISTON AND TO BLOCK SAID FLUID PASSAGE THERETHROUGH, SAID PISTON ROD ANDSAID MOVABLE CONTACT MEANS BEING ADAPTED TO ABUT EACH OTHER IN CONTACTCLOSED POSITION, SAID MOVABLE CONTACT MEANS BEING OPERATIVE DURINGCIRCUIT CLOSING MOVEMENT TO MOVE THROUGH SAID OPENING IN SAID END WALLTO ABUT SAID PISTON ROD AND DRIVE SAID PISTON ROD AND SAID PISTON TOTHEIR BIASED POSITIONS SO THAT DURING A CIRCUIT OPENING OPERATION SAIDPISTON MOVES IN CONTACT OPENING DIRECTION FOR BLASTING FLUIDTRANSVERSELY THROUGH THE SPACE BETWEEN SAID STATIONARY CONTACT MEANS ANDSAID OPENING AND AXIALLY THROUGH SAID OPENING, SAID PISTON ROD BEINGINDEPENDENTLY MOVABLE DURING A CIRCUIT OPENING OPERATION TO ACCELERATESAID MOVABLE CONTACT MEANS.